The heritability of many diseases is well defined. Accordingly, information about relatives and their health or disease has become an essential part of history-taking in the process of medical diagnosis. However, it has been difficult to use such information about family history (or more generally all forms of history about “transmission” of diseases) in computerized medical diagnostic tools. In part, this is because of the complexity of medical genetics in which many different forms of inheritance are possible however, another significant barrier are other difficulties in representing such transmission history. There are 6 main types of inheritance patterns for diseases that have been well described in the medical literature:                1. Autosomal dominant: a gene on a non-sex chromosome causes disease when one copy is defective. If one parent has such a gene, each child typically has a 0.5 chance of getting the disease.        2. Autosomal recessive: a gene on a non-sex chromosome causes disease when both copies are defective. If both parents have such a gene, each child typically has a 0.25 chance of getting the disease.        3. X-linked dominant: a gene on an X chromosome causes disease when one copy is defective. Males typically have one X chromosome, females typically have two. Females typically get an X chromosome from each parent, males typically get one only from the mother.        4. X-linked recessive: a gene on an X chromosome causes disease when all copies are defective (typically one for males and two for females). Females typically get an X chromosome from each parent, males typically get one only from the mother.        5. Mitochondrial (dominant): a mitochondrial gene causes disease when a high percentage of copies are defective. Mitochondrial genes come essentially only from the mother.        6. Y-linked (dominant): a gene on the Y chromosome causes disease when defective. Only males have Y chromosomes and they are inherited from the father.These forms of transmission are further complicated by:        Spontaneous mutation—appearance of a genetic defect despite the presence of a normal gene genes in parents.        Penetrance—not all people with a pathogenic number of defective genes exhibit the disease. The fraction who exhibit the disease is called penetrance.        Consanguinity—close genetic relationship of parents, for example first cousins, increasing the chance of recessive diseases.        Non-paternity or other false reports of family history.In addition, transmission can be environmental or contagious.        